I would like to know correct way of changing Enabled property of dfm component based on other components state.
For example, I have edit3 that should be enabled only if value of some edit1 is in set of {'value1', 'value2'} and edit2 value is 'edit2Val'
What is the most correct way to do this?
Or is there better way then to make 2 onChange events which will look like this?
procedure tFrm1.edit1Change(Sender : TObject);
begin
edit3ChangeEnabled;
//some specific code
end;
procedure tFrm1.edit2Change(Sender : TObject);
begin
edit3ChangeEnabled;
//some other specific code
end;
procedure tFrm1.edit3ChangeEnabled;
var
Enabled : Boolean;
begin
Enabled := checkEdit1Vals and checkEdit2Vals;
edit3.Enabled := Enabled;
end;
Related
In some applications, like Microsoft Excel, the dot-key from the numeric keypad (VK_DECIMAL) is automatically converted into the current DecimalSeparator.
I'm trying to implement the same feature but I didn't find a way to make it work in the whole application.
At the form level, it can be done by using the form's KeyPreview property and OnKeyPress event handler, for example:
function IsKeyPressed(const AKey : Word) : Boolean;
begin
Result := GetKeyState(AKey) < 0;
end;
procedure TMyBaseForm.FormCreate(Sender: TObject);
begin
inherited;
KeyPreview := True;
end;
procedure TMyBaseForm.FormKeyPress(Sender: TObject; var Key: Char);
begin
inherited;
if(IsKeyPressed(VK_DECIMAL))
then Key := FormatSettings.DecimalSeparator;
end;
But this solution requires to have a common base form class for all application's forms and won't work with any form/dialog who is not inheriting from that base class (i.e: It will not work with a simple InputQuery either)
I am super newbie and tried to write following code which sets every TEdit.Text to one mentioned in code
procedure TForm2.Button1Click(Sender: TObject);
var
i : integer;
Edit : TEdit;
begin
for i := 0 to Edit.ComponentCount - 1 do
begin
with Edit.Components[i] do
begin
Text := 'Done';
end;
end;
end;
What am I doing wrong ?
Here are the mistakes that I can see:
You never assign a value to Edit.
Typically the form owns all the components, and so a TEdit will have zero owned components.
Edit.Components[i] is of type TComponent which does not have a Text property. If your code compiles, then Text is actually that of the form. The lesson you should learn from this point is never to use with ever again.
You should solve this using code like this:
procedure TForm2.Button1Click(Sender: TObject);
var
i: Integer;
Edit: TEdit;
begin
for i := 0 to ComponentCount-1 do begin
if Components[i] is TEdit then begin
Edit := TEdit(Components[i]);
Edit.Text := 'Done';
end;
end;
end;
Note that here we are using ComponentCount and Components[] from the form itself. We have removed the evil with statement. And we have had to cast the component to a reference of type TEdit, after first using the is operator to check the type of the component.
This approach will work so long as the form owns all the edits found within it. However, if you create controls dynamically, or if you use frames or parented forms, then this approach, based on ownership via Components[] will not yield all the controls. In such more complex cases you would need to iterate using the parent/child relationship using ControlCount and Controls[].
What am I doing wrong? Just about everything. What I think you are trying to achieve is to put the same text in all TEdits on the form. So you need to go through all the components in TForm (not Edit!) and and check that each is really a Tedit, and if so assign the text. Like this:
procedure TForm2.Button1Click(Sender: TObject);
var
i:integer;
begin
for i := 0 to ComponentCount - 1 do
begin
if Components[ I ] is TEdit then
begin
(Components[ I ] as TEdit).Text := 'Done';
end;
end;
end;
As an aside - avoid using 'with'. It just cases ambiguity and confusion.
You could iterate over all child controls of the form, and if the current control is a TEdit, then you set its text. If the current control is a windowed control, it might have child controls of its own, and you need to redo same thing for this control. Hence, let's use recursion:
procedure SetAllEdits(AParent: TWinControl; const AText: string);
var
i: Integer;
begin
for i := 0 to AParent.ControlCount - 1 do
if AParent.Controls[i] is TCustomEdit then
TCustomEdit(AParent.Controls[i]).Text := AText
else if AParent.Controls[i] is TWinControl then
SetAllEdits(TWinControl(AParent.Controls[i]), AText);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
SetAllEdits(Self, 'test');
end;
There are other ways, like subclassing the edit control and having the new class respond to broadcasted messages.
Answer from D. Heffernan is already good, I'm trying to make it easier to understand for beginner.
In this code, we do "typecast" TEdit to TComponent by command: aEdit := TEdit(aComponent), because TEdit is inherited from TComponent.
What you get from iteration (for ...) is TComponent, not TEdit. You get TEdit by "typecast" it.
procedure TForm2.Button1Click(Sender: TObject);
var
i : Integer;
aComponent : TComponent;
aEdit : TEdit;
begin
for i := 0 to ComponentCount-1 do
begin
aComponent := Components[i];
if aComponent is TEdit then
begin
aEdit := TEdit(aComponent);
aEdit.Text := 'Done';
end;
end;
end;
I have added hints to components on my form. When the components receive the focus, I'd like to set the caption of a label component to display the hint.
I have added a TApplicationEvents object and set the OnShowHint event to
procedure TImportFrm.ApplicationEvents1ShowHint(var HintStr: string;
var CanShow: Boolean; var HintInfo: THintInfo);
begin
HelpLbl.Caption := HintStr;
end;
However it seems that the ShowHint event only fires with mouse movements. Is there a way to fire the hint code when components receive focus, without having to implement the OnEnter event for every single component on the form?
Add a handler for TScreen.OnActiveControlChange in your main form's creation, and handle the hints in that event:
type
TForm2=class(TForm)
...
private
procedure ScreenFocusControlChange(Sender: TObject);
end;
implementation
procedure TForm2.FormCreate(Sender: TObject);
begin
Screen.OnActiveControlChange := ScreenFocusControlChange;
end;
procedure TForm2.ScreenFocusControlChange(Sender: TObject);
begin
Label1.Caption := ActiveControl.Hint;
Label1.Update;
end;
Note that Sender won't do you much good; it's always Screen. You can filter (for instance, to only change the Label.Caption for edit controls) by testing the ActiveControl:
if (ActiveControl is TEdit) then
// Update caption of label with ActiveControl.Hint
Note that if you'll need to reassign the event when you show child forms (to an event on that child form), or you'll always be updating the original form's label with the hints. The easiest way to do the reassignment is to give every form an OnActiveControlChange handler, and assign it in the form's OnActivate event and unassign it in the OnDeactivate event:
procedure TForm1.FormActivate(Sender: TObject);
begin
Screen.OnActiveControlChange := Self.ScreenActiveControlChange;
end;
procedure TForm1.FormDeactivate(Sender: TObject);
begin
Screen.OnActiveControlChange := nil;
end;
This will allow you to update controls other than Label1 on each form, and only use the hint changes on forms you want to do so.
A simple solution is to use OnIdle event:
procedure TForm1.ApplicationEvents1Idle(Sender: TObject; var Done: Boolean);
begin
if Assigned(ActiveControl) then
Label1.Caption:= ActiveControl.Hint;
end;
A more advanced solution is to override protected ActiveChanged method of TForm:
type
TForm1 = class(TForm)
...
protected
procedure ActiveChanged; override;
end;
...
procedure TForm1.ActiveChanged;
begin
inherited;
if Assigned(ActiveControl) then
Label1.Caption:= ActiveControl.Hint;
end;
Receiving focus and OnShowHint are quite different events; OnShowHint can be triggered for non-focused control as well.
Why would you need to implement the OnEnter event for every single component? You can create one generic method / event handler like:
procedure TForm1.AnyControlEnter(Sender: TObject);
begin
lbl1.Caption := TControl(Sender).Hint;
end;
and assign it to every component you placed on the form.
You said:
it seems that the ShowHint event only fires with mouse movements
This is a normal behaviour. The problem you have ( it's a guess) is that hints are not fired directly. Don't try to make a workaround, what you try to do with MouseEnter is exactly what is already happening...the only difference is that you'be forget something...
Keep the event ApplicationEvents1ShowHint() as you've initially done but add this in the form constructor event:
Application.HintPause := 1;
And then hints will be displayed (almost) without delay.
What can I do that shortcuts for menu items don't overwrite those from local controls?
Imagine this simple app in the screenshot. It has one "undo" menu item with the shortcut CTRL+Z (Strg+Z in German) assigned to it. When I edit some text in the memo and press CTRL+Z I assume that the last input in the memo is reverted, but instead the menu item is executed.
This is especially bad in this fictional application because the undo function will now delete my last added "Item 3" which properties I was editing.
CTRL+Z is just an example. Other popular shortcuts cause similar problems (Copy&Paste: CTRL+X/C/V, Select all: CTRL+A).
Mini Demo with menu item with CTRL+Z short-cut http://img31.imageshack.us/img31/9074/ctrlzproblem.png
The VCL is designed to give menu item shortcuts precedence. You can, however, write your item click handler (or action execute handler) to do some special handling when ActiveControl is TCustomEdit (call Undo, etc.)
Edit: I understand you don't like handling all possible special cases in many places in your code (all menu item or action handlers). I'm afraid I can't give you a completely satisfactory answer but perhaps this will help you find a bit more generic solution. Try the following OnShortCut event handler on your form:
procedure TMyForm.FormShortCut(var Msg: TWMKey; var Handled: Boolean);
var
Message: TMessage absolute Msg;
Shift: TShiftState;
begin
Handled := False;
if ActiveControl is TCustomEdit then
begin
Shift := KeyDataToShiftState(Msg.KeyData);
// add more cases if needed
Handled := (Shift = [ssCtrl]) and (Msg.CharCode in [Ord('C'), Ord('X'), Ord('V'), Ord('Z')]);
if Handled then
TCustomEdit(ActiveControl).DefaultHandler(Message);
end
else if ActiveControl is ... then ... // add more cases as needed
end;
You could also override IsShortCut method in a similar way and derive your project's forms from this new TCustomForm descendant.
You probably need an alike solution as below. Yes, feels cumbersome but this is the easiest way I could think of at the time. If only Delphi allowed duck-typing!
{ you need to derive a class supporting this interface
for every distinct control type your UI contains }
IEditOperations = interface(IInterface)
['{C5342AAA-6D62-4654-BF73-B767267CB583}']
function CanCut: boolean;
function CanCopy: boolean;
function CanPaste: boolean;
function CanDelete: boolean;
function CanUndo: boolean;
function CanRedo: boolean;
function CanSelectAll: Boolean;
procedure CutToClipBoard;
procedure Paste;
procedure CopyToClipboard;
procedure Delete;
procedure Undo;
procedure Redo;
procedure SelectAll;
end;
// actions....
procedure TMainDataModule.actEditCutUpdate(Sender: TObject);
var intf: IEditOperations;
begin
if Supports(Screen.ActiveControl, IEditOperations, intf) then
(Sender as TAction).Enabled := intf.CanCut
else
(Sender as TAction).Enabled := False;
end;
procedure TMainDataModule.actEditCutExecute(Sender: TObject);
var intf: IEditOperations;
begin
if Supports(Screen.ActiveControl, IEditOperations, intf) then
intf.CutToClipBoard;
end;
....
I've got a pretty big setup form which I'd like to populate with data from a class. so I'm doing a lot of
Edt1.text := ASettings.FirstThing;
I'd like to avoid
Edt1.onchange := nil;
Edt1.text := ASettings.FirstThing;
Edt1.onchange := edt1Onchange;
How do I change the text in a text box and sidestep the onchange event.
I have used something like changing the OnChange handler, but more often, I use a flag.
updatingFromCode := true;
Edt1.Text := ASettings.FirstThing;
updatingFromCode := false;
then
procedure TForm1.OnChange(...);
begin
if updatingFromCode then
Exit;
...
Also, rather than hardcoding the OnChange the the actual OnChange procedure, I would store the Edit control's current value, then reset it (which will work if it is not set, or if another place has changed it, etc.)
oldOnChange := Edt1.OnChange;
Edt1.OnChange := nil;
Edt1.Text := ASettings.FirstThing;
Edt1.OnChange := oldOnChange;
You might consider using an object to manage the NIL'ing of the event and restoring the previously installed event handler. It's a little dangerous to assume that the event to be restored just happens to be the one assigned at design-time/which happens to have the "name that fits" - you should always save/restore the currently assigned handler, just to be safe.
This would provide an even more re-usable utility than the SetTextWithoutOnChange() routine:
TSuspendEvent = class
private
fObject: TObject;
fEvent: String;
fHandler: TMethod;
public
constructor Create(const aObject: TObject; aEvent: String);
destructor Destroy; override;
end;
constructor TSuspendEvent.Create(const aObject: TObject; aEvent: String);
const
NILEvent : TMethod = (Code: NIL; Data: NIL);
begin
inherited Create;
fObject := aObject;
fEvent := aEvent;
fHandler := GetMethodProp(aObject, aEvent);
SetMethodProp(aObject, aEvent, NILEvent);
end;
destructor TSuspendEvent.Destroy;
begin
SetMethodProp(fObject, fEvent, fHandler);
inherited;
end;
In usage, this would look something like:
with TSuspendEvent.Create(Edit1, 'OnChange') do
try
Edit1.Text := 'Reset!';
finally
Free;
end;
For the "Thou shalt not use 'with' crowd" - by all means declare yourself an additional local variable and use that if it will help you sleep easier at night. :)
Or, to make it even more convenient to use and eliminate "with", I would make the TSuspendEvent class an interfaced object and wrap its use in a function that yielded an interface reference to it that could be allowed to "live in scope", as exemplified by my AutoFree() implementation. In fact, you could use AutoFree() as-is to manage this already:
AutoFree(TSuspendEvent.Create(Edit1, 'OnChange'));
Edit1.Text := 'Reset!';
Dsabling events for a period that extends beyond the scope of a single procedure requires more management than any helper utilities are likely to be able to provide in a generic fashion I think, at least not without also having specific means for restoring events explicitly, rather than automatically.
If you simply wrapped TSuspendEvent inside it's own interface yielding function, following the same pattern as AutoFree() you could simplify this further to:
SuspendEvent(Edit1, 'OnChange');
Edit1.Text := 'Reset!';
As a final note, I think it should be fairly easy to see how this could be quite simply extended to support suspending multiple events on an object in a single call, if required, for example:
SuspendEvent(Edit1, ['OnChange', 'OnEnter']);
As far as I know if the OnChange of your object is designed to fire when the Text property is changed you have to stick with setting the event to nil temporarly. Myself, I do it this way (in a try finally):
Edt1.onchange := nil;
try
Edt1.text := ASettings.FirstThing;
finally
Edt1.onchange := edt1Onchange;
end;
You could also do some procedure to handle it for you:
procedure SetTextWithoutOnChange(anEdit: TEdit; str: String);
var
anEvent: TNotifyEvent;
begin
anEvent := anEdit.OnChange;
anEdit.OnChange := nil;
try
anEdit.Text := str;
finally
anEdit.OnChange := anEvent;
end;
end;
I know this is an old question but I thought I would add my solution that does not involve any of the complicated procedures outlined in the previous answers in case it comes up in another search.
The problem is the onChange event itself. I don't use it at all for text fields.
remove all OnChange and use the OnExit instead and tie it to the OnKeyUp.
All Edits have a common ancestor TCustomEdit.
I generally use one method called CustomEditKeyUp and point all the edits on a form to this single method (TEdit, TLabeledEdit etc etc.)
type THack = class(TCustomEdit);
procedure TForm1.CustomeEditKeyUP(Sender: TObject; var Key: Word;
Shift: TShiftState);
begin
if (Key=VK_RETURN) and (Sender is TCustomEdit) then
{This is just to isolate the one occasion when they press the
enter but don't exit immediately}
if Assigned(THack(Sender).OnExit) then THack(Sender).OnExit(Sender);
end;
For some reason, the OnExit is private in a TCustomEdit so the Hack is needed. If you know that the edits are from a different route where the OnExit is public, cast if differently and the Hack is not necessary.
Then For each Edit control, use a specific OnExit
procedure TForm1.MyEditExit(Sender: TObject);
begin
if MyEdit.Modified then
begin
{Do Something here}
MyEdit.Modified := false;
end;
end;
If you want to change the value programmatically without it firing 'OnExit'
....
MyEdit.Text :='I've changed it'
MyEdit.Modified := false;
....
The big advantage for me is that when I am parsing the input for say a valid number, I only have to do this once when editing is completed and not for every single backspace, delete insert etc all surrounded by try except as the various formating functions error out as they don't understand spaces etc.. For database etc, the number of calls will be greatly reduced.
That's my two penneth.
Another way is by using Class Helpers introduced in Delphi 8.
http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Class_and_Record_Helpers_(Delphi)
You could write:
type
TEditHelper = class helper for TEdit
public
procedure SetTextDisableOnChange(const AText: string);
end;
{ TEditHelper }
procedure TEditHelper.SetTextDisableOnChange(const AText: string);
var
OnChangeTmp: TNotifyEvent;
begin
OnChangeTmp:=OnChange;
try
OnChange:=nil;
Text:=AText;
finally
OnChange:=OnChangeTmp;
end;
end;
and then:
EditCtrl.SetTextDisableOnChange('I do not invoke OnChange!');
EditCtrl.Text:='I invoke OnChange';